In recent years, semiconductor lasers have been used in various technical fields. For example, they are used as light sources in an optical disc recording/reproducing apparatus, a display apparatus such as a laser display or the like, a laser printer apparatus, and a light communicating apparatus.
Hitherto, semiconductor lasers of an AlGaAs system, AlGaInAs system, and AlGaInP system have already been commercialized as such semiconductor lasers. In recent years, it is demanded to commercialize a semiconductor laser of a GaN/GaInN system which can emit a laser beam of a further short wavelength. It has been proposed to use such a GaN/GaInN system semiconductor in an optical system for recording/reproducing, for example, a high density optical disc (Blu-ray Disc) of the next generation.
The semiconductor laser is generally enclosed in a package in order to prevent adhesion of impurities or the like and various kinds of packages are used. Among them, a CAN package is one of the most widely used packages.
An assembling method of the conventional CAN package light emitting device will now be described herein below with reference to FIGS. 10A, 10B, 11A, 11B, 12A, and 12B.
<Chip Mounting Step>
First, as shown in FIG. 1A, a semiconductor laser 101 such as AlGaAs system semiconductor laser of a band of 790 nm, AlGaInP system semiconductor laser of a band of 650 nm, or the like is adhered to a predetermined position on a submount 102 by a Sn solder.
<Die-Bonding Step>
Subsequently, as shown in FIG. 10B, the submount 102 is die-bonded to a predetermined position on a heat sink 105 provided for a fixed plate 104. In this instance, an Ag paste is used as an adhesive agent 103.
<Paste Hardening Step>
Subsequently, as shown in FIG. 11A, the adhesive agent 103 is hardened.
<Wire-bonding Step>
Subsequently, as shown in FIG. 11B, the submount 102 and a lead pin 106b are connected by an Au wire 107.
<Sealing Step>
Subsequently, as shown in FIG. 12A, a cap 108 is electrically welded to the fixed plate 104 in an oxygen (dry oxygen) atmosphere from which moisture (H2O) has been removed. Thus, as shown in FIG. 12B, the CAN package light emitting device in which dry oxygen has been sealed is completed. In the sealing step, as a gas (substitute gas) which is sealed in the CAN package light emitting device besides dry oxygen, a N2 (nitrogen) gas, an Ar (argon) gas, a He (helium) gas, or mixture gases consisting of N2 and O2 is generally used.
Although rarely disclosed because of a recognition as know-how, there is a deteriorating mechanism which is caused by reactive growth between gases which are generated from installed parts and their materials. Besides electric energy, heat energy and light energy can be mentioned as energy sources. It has been known that a method of properly selecting the substitute gas is effective as a countermeasure for such a deteriorating mechanism.
According to the knowledge of the inventors of the present invention, if the CAN package light emitting device having the GaN/GaInN system semiconductor laser of the 405 nm band is manufactured by the assembling method mentioned above, there is such a problem that in such a light emitting device, a deposit is formed in a light emitting portion of the semiconductor laser 101 and a drive current fluctuates periodically in accordance with a driving time.
Therefore, the inventors of the present invention have examined in order to investigate the causes of the creation of such a deposit, so that they obtained the following knowledge.                (1) The deposit is formed only in the light emitting portion when the semiconductor laser 101 is driven. Therefore, the creation of the deposit is a reaction concerned with light.        (2) The Ag paste is not directly come into contact with the semiconductor laser 101. Further, no Ag is contained in the deposit. Therefore, the creation of the deposit is not caused by such a phenomenon that the Ag paste is diffused into the semiconductor laser 101.        
The inventors of the present invention have made a further examination on the basis of the above knowledge, so that they found out that an Si organic compound gas which is generated from the Ag paste and an Si organic compound gas adhered to the fixed plate 104 reach the light emitting portion of the semiconductor laser 101 and react on an emitted laser beam, so that the deposit is formed.
Therefore, to prevent the deposit from being formed in the light emitting portion of the semiconductor laser 101, in the assembling method of the conventional CAN package light emitting device, the applicant of the present invention proposes an assembling method of a light emitting device whereby an ozone cleaning step is provided between the wire bonding step and the sealing step.
FIG. 13 shows the ozone cleaning step proposed by the applicant of the present invention. In the ozone cleaning step, as shown in FIG. 13, while supplying an ozone (O3) gas, ultraviolet rays are irradiated to the fixed plate 104 by a xenon lamp. Thus, activated ozone collides with a surface of the Ag paste and a surface of the fixed plate 104 and an Si organic compound is decomposed. An Si element is converted into SiO2 and becomes a stable substance. A hydro carbon portion of an alkyl group or the like is decomposed to CO, CO2, or H2O.
However, according to the above assembling method, such a problem that parts of the fixed plate 104, the semiconductor laser 101, and the like are polluted again by the Si organic compound gas before sealing occurs. Such recontamination is particularly conspicuous in the case where the step using the Ag paste exists on the processes from the cleaning step to the sealing step or in the case where a staying period of time from the completion of the cleaning to the sealing is long.
As a method of avoiding the recontamination, there are considered (1) a method of promptly sealing after the ozone cleaning and (2) a method of realizing such an environment that no Si organic compound gas is adhered onto the fixed plate or the like before sealing. However, if such time-dependent and environmental limitations are provided in the steps, such a problem that mass-productivity deteriorates is caused.